Temperature dependence of creep and recovery behaviors of polymer composites filled with chemically reduced graphene oxide

Resistance to time-dependent plastic deformation of polymer composite materials is a crucial requirement in their application for long-term durability and reliability. Herein, creep and recovery behaviors of polystyrene (PS) composites filled with various loadings of chemically reduced graphene oxide (CRGO) were investigated at different environment temperatures. As expected, incorporation of CRGO into PS polymer increases the thermal stability, glass transition temperature and elastic modulus, although the tensile strength of the composite has a slight decrease. It was found that the creep deformation and strain rate of PS polymer reduce with decreasing temperature and with increasing loading of CRGO. A significant improvement in the recovered strain of PS was also obtained after the presence of CRGO. Based on the analytical modelings (Burger’s model and Weibull distribution function) and experimental results, the role of CRGO on improving the creep and recovery performance of thermoplastics was proposed and discussed.     

Production of reduced graphene oxide by UV irradiation

Herein, we report on a self-photocatalytic reduction (SPCR) strategy toward the production of reduced graphene oxide (GO), carried out by UV irradiation of GO dispersion in the presence of N,N-dimethylformamide (DMF) serving as an electron donor (ED). It is found that a stable dispersion of rGO is produced by UV irradiation of GO solution in the presence of DMF. The use of natural sunlight as driving force for such SPCR reaction is also demonstrated.     

Ambient flash sintering of reduced graphene oxide/zirconia composites:Role of reduced graphene oxide

Fabrication of graphene/ceramic composites commonly requires a high-temperature sintering step with long times as well as a vacuum or inert atmosphere,which not only results in property degradation but also significant equipment complexity and manufacturing costs.In this work,the ambient flash sintering behavior of reduced graphene oxide/3 mol% yttria-stabilized ZrO₂(rGO/3 YSZ) composites utilizing rGO as both a composite component and a conductive additive is reported.When the sintering condition is carefully optimized,a dense and conductive composite can be achieved at room temperature and in the air within 20 s.The role of the rGO in the FS of the rGO/3 YSZ composites is elucidated,especially with the assistance of a separate investigation on the thermal runaway behavior of the rGO.The work suggests a promising fabrication route for rGO/ceramic composites where the vacuum and furnace are not needed,which is of interest in terms of simplifying the fabrication equipment for energy and cost savings.     

Fibers of reduced graphene oxide nanoribbons

Reduced graphene oxide nanoribbon fibers were fabricated by using an electrophoretic self-assembly method without the use of any polymer or surfactant. We report electrical and field emission properties of the fibers as a function of reduction degree. In particular, the thermally annealed fiber showed superior field emission performance with a low potential for field emission (0.7?V?μm(-1)) and a giant field emission current density (400?A?cm(-2)). Moreover, the fiber maintains a high current level of 300?A?cm(-2) corresponding to 1?mA during long-term operation.     

Appropriate conditions for preparing few-layered graphene oxide and reduced graphene oxide

Oxidation time and exfoliated conditions of graphite oxides (GOs) were investigated to prepare few–layer graphene oxide and reduced graphene oxide via a modified Hummers approach. Different oxidative degree of GOs was prepared by changing oxidation time, and the effects of oxidative degree of GOs in different oxidation time were studied by XRD, FT-IR. Afterwards, highly oxidized GOs were used as precursor to prepare graphene oxide and reduced graphene oxide by ultrasonic dispersion method and thermal expansion method. The exfoliated conditions (ultrasonic power and ultrasonic time, thermal exfoliated temperature) were investigated to prepare few-layered graphene oxide and reduced graphene oxide.     

P-type reduced graphene oxide membranes induced by iodine doping

Reduced graphene oxide membranes with electrical conductivity of 201 S/cm were successfully fabricated by a simple hydriodic acid reducing method. It has been shown that the obtained graphene oxide membranes exhibit a p-type conductive property with a hole carrier concentration of 3.66 × 10¹⁷ cm^?2 and a mobility of 13.7 cm²/Vs. The p-type conductive property was mainly attributed to iodine atom adsorption on C atom layer, supported by the energy dispersive X-ray spectrometry and the first-principles calculations based on the density functional theory. The Bader method was used to analyze charge density of each atom. It has been shown that 0.38 electrons per unit cell are transferred to I atom from the C atom layer which leaves a lot of holes.     

Spectroscopic studies of large sheets of graphene oxide and reduced graphene oxide monolayers prepared by Langmuir-Blodgett technique

Graphene oxide (GO) sheets prepared by chemical exfoliation were spread at the air-water interface and transferred to silicon substrates by Langmuir-Blodgett technique as closely spaced monolayers of 20-40 μm size. Hydrazine exposure followed by annealing in vacuum and argon ambient results in the formation of reduced graphene oxide (RGO) monolayers, without significantly affecting the overall morphology of the sheets. The monolayer character of both GO and RGO sheets was ascertained by atomic force microscopy. X-ray photoelectron spectroscopy supported by Fourier transform infrared spectroscopy revealed that the reduction process results in a significant decrease in oxygen functionalities, accompanied by a substantial decrease in the ratio of non-graphitic to graphitic (sp² bonded) carbon in the monolayers from 1.2 to 0.35. Raman spectra of GO and RGO monolayers have shown that during the reduction process, the G-band shifts by 8-12 cm^− 1 and the ratio of the intensities of D-band to G-band, I(D)/I(G) decreases from 1.3 ± 0.3 to 0.8 ± 0.2, which is in tune with the smaller non-graphitic carbon content of RGO monolayers. The significant decrease in I(D)/I(G) has been explained by assuming that substantial order is present in precursor GO monolayers as well as RGO monolayers obtained by solid state reduction.     

Electrochemical determination of hydrazine based on polydopamine-reduced graphene oxide nanocomposite

In this work, a simple and mild procedure was employed to synthesize polydopamine-reduced graphene oxide (PDA-RGO) nanocomposites, where the sheets of graphene oxide were functionalized firstly with PDA through self-polymerization. FTIR was used to confirm that the GO sheets had been functionalized successfully with PDA and reduced. Besides, UV-Vis and X-ray diffraction spectroscopy were employed to further demonstrate the formation of RGO. The electrochemical property of the PDA-RGO has been studied by the determination of hydrazine. The results indicated that the electrochemical oxidation of hydrazine was significantly improved by the obtained PDA-RGO nanocomposite due to the increased available surface area of electrode. A quick amperometric response was observed with the electrochemical sensor based on PDA-RGO nanocomposite for the hydrazine measurement in a wide linear range of 0.03–100 μM, where the limit of the detection was 0.01 μM.     

Size dependence electrocatalytic activity of gold nanoparticles decorated reduced graphene oxide for hydrogen evolution reaction

It is promising for AuNPs/RGO composites to be exploited for hydrogen evolution reaction (HER), due to the collaborative effects between the electrocatalytic Au nanoparticles (AuNPs) and conductive reduced graphene oxide (RGO). In this work, we used a simple way to decorate AuNPs onto the RGO surface by one pot in situ reduction both HAuCl₄ and GO, for which the controlled average size of AuNPs (2.7, 11.5 and 45.7 nm) is adjusting with the mass ratio of HAuCl₄ and GO. The obtained materials, AuNPs/RGO composites, show excellent electrocatalytic activity for the HER that critical dependence on the particle size of AuNPs. The results show that AuNPs/RGO with AuNPs size of 11.5 nm exhibits superior electrochemical activity: low onset potential of 0.029 V versus the reversible hydrogen electrode as well as a small Tafel slope of 86 mV per decade.     

Infrared photodetectors based on reduced graphene oxide and graphene nanoribbons

The use of reduced graphene oxide (RGO) and graphene nanoribbons (GNRs) as infrared photodetectors is explored, based on recent results dealing with solar cells, light-emitting devices, photodetectors, and ultrafast lasers. IR detection is demonstrated by both RGO and GNRs in terms of the time-resolved photocurrent and photoresponse. The responsivity of the detectors and their functioning are presented.     

Hydrothermal synthesis of magnetic reduced graphene oxide sheets

We demonstrated an environmental friendly and efficient route for preparation of magnetic reduced graphene oxide composite (MN-CCG). Glucose was used as the reducing agent in this one-step hydrothermal method. The reducing process was accompanied by generation of magnetic nanoparticles. The structure and composition of the nanocomposite was confirmed by Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction, thermal gravimetric analysis, atomic force microscopy and transmission electron microscopy. It was found that the prepared MN-CCG is highly water suspendable and sensitive to magnetic field.     

Temperature dependence of the Raman spectra of graphene and graphene multilayers

We investigated the temperature dependence of the frequency of G peak in the Raman spectra of graphene on Si/SiO2 substrates. The micro-Raman spectroscopy was carried out under the 488 nm laser excitation over the temperature range from -190 to +100 degrees C. The extracted value of the temperature coefficient of G mode of graphene is chi = -0.016 cm-1/ degrees C for the single layer and chi = -0.015 cm-1/ degrees C for the bilayer. The obtained results shed light on the anharmonic properties of graphene.     

Wafer-scale reduced graphene oxide films for nanomechanical devices

We report a process to form large-area, few-monolayer graphene oxide films and then recover the outstanding mechanical properties found in graphene to fabricate high Young's modulus ( =185 GPa), low-density nanomechanical resonators. Wafer-scale films as thin as 4 nm are sufficiently robust that they can be delaminated intact and resuspended on a bed of pillars or field of holes. From these films, we demonstrate radio frequency resonators with quality factors (up to 4000) and figures of merit ( f x Q>10(11)) well exceeding those of pure graphene resonators reported to date. These films' ability to withstand high in-plane tension (up to 5 N/m) as well as their high Q-values reveals that film integrity is enhanced by platelet-platelet bonding unavailable in pure graphite.     

Microwave surface impedance measurements on reduced graphene oxide

Here we report a non-contact method for microwave surface impedance measurements of reduced graphene oxide samples using a high Q dielectric resonator perturbation technique, with the aim of studying the water content of graphene oxide flakes. Measurements are made before, during and after heating and cooling cycles. We have modelled plane wave propagation of microwaves perpendicular to the surface of graphene on quartz substrates, capacitively coupled to a dielectric resonator. Analytical solutions are derived for both changes in resonant frequency and microwave loss for a range of water layer thicknesses. In this way we have measured the presence of adsorbed water layers in reduced graphene oxide films. The water can be removed by low temperature annealing on both single and multilayer samples. The results indicate that water is intercalated between the layers in a multilayer sample, rather than only being adsorbed on the outer surfaces, and it can be released by applying a mild heating.     

A review of top-down and bottom-up synthesis methods for the production of graphene,graphene oxide and reduced graphene oxide

Journal of Materials Science - As nanotechnology floods application areas like medicine, electronics, water remediation, space and textiles, just to name a few, some nanomaterials remain in the...     

High-strength reduced graphene oxide paper prepared by a simple and efficient method

Journal of Materials Science - Excellent mechanical and electrical properties of graphene-based paper-like materials are essential for applications in flexible conductors, energy-storage devices,...     

Transparent, luminescent, antibacterial and patternable film forming composites of graphene oxide/reduced graphene oxide

Multifunctional graphene oxide/reduced graphene oxide (GO/RGO) composites were prepared through electrostatic interaction using biocompatible ingredients. Different functionalities were added to GO/RGO by anchoring materials such as native lactoferrin (NLf), NLf protected Au clusters (designated as Au@NLf), chitosan (Ch) and combinations thereof. Anchoring of Ch and NLf enhances the antibacterial property of RGO/GO. The addition of Ch to RGO/GO not only helped in forming stable dispersions but also helped in fabricating large (cm(2)) area films through a simple solvent evaporation technique. Functionalities such as photoluminescence were added to Ch-RGO/GO composites by anchoring Au@NLf on it. The composites thus formed showed stable luminescence in presence of various metal ions in the solid state. The composite showed reasonable stability against pH and temperature variations as well. The as-prepared films were transparent and the transparency could be modulated by controlling the concentration of RGO/GO in the composite. The antibacterial property and ability to form stable thin films may provide an opportunity to use such composites for medical and environmental remediation applications as well. Erasable patterns were fabricated on the film by stamping required patterns under compressive pressure. Luminescent patterns can be inscribed on the film and can be erased by simply wetting it. Such films with erasable information may be useful for security applications.